User mobility enables users to switch between end devices and still get the same, personal services. These services include the access to one's personal data, the availability of a personal collection of customized services, and the transparent reachability at the same user address. Personal addressing requires an infrastructure that (a) intercepts calls to (static) user addresses and (b) dynamically maps a user address to one or several devices addresses. The possible degree of flexibility and intelligence of this mapping depends to a large extent on the infrastructure's knowledge of the potential terminating end devices. In case of fixed wire phones, to know whether the phone is currently on-hook or off-hook helps, e.g., to not route the call to a busy phone but to another device. In case of mobile phones, the range of potentially available status and configuration information is much broader. It can include registration and location information, the actual availability status, and the phone's value added service settings such as call forwarding activation, barring of incoming calls, do not disturb, etc. The more information the infrastructure can draw on, the more intelligent the destination selection process can be. A system that can take advantage of all the above information—and thus integrates terminal and user mobility—is called a global roaming infrastructure.
Such an infrastructure requires a notion of a user who can own multiple (fixed wired and wireless) devices, and it needs to model and manage an appropriate subscriber base. Even if this subscriber base is realized as a federated database comprising separate, traditional subscriber bases, such as the Home Location Registers (HLR) in cellular networks, it requires a unifying subscriber data view as well as the storage of novel, global roaming supporting entities. The implementation of a multi-technology subscriber base as one integrated database, is beneficial with respect to storage efficiency as well as data plausibility. Of course, integration does not equal centralization and, in fact, one implementation of the present invention is highly distributed over multiple network elements. What is needed is an appropriate model for a global roaming subscriber base.